The present invention relates to a method and apparatus for controlling the flow cut-off of molten metal in a foundry installation wherein a ladle pours molten metal into successive molds each provided with a sprue cup.
In foundry installations which effect the filling in series of individual sand or permanent molds which are closed and provided with a sprue cup, the control for cutting-off the casting ladle at the time when the mold is full is important since it determines the quality of the molded article, the safety of the operation, the regular course of the casting operations, as well as the amount of metal wasted. In point of fact, it is of decisive importance that the stopping of the pouring of the mold be brought about only at the moment when the mold is actually full, in order to avoid rejects due to lack of material within the mold. On the other hand, it is necessary to avoid the control being effected too late and the mold overflowing from its sprue cup which on the one hand might be dangerous and on the other hand require the interruption of the pouring operations and possibly the additional operations of freeing or cleaning the area where pouring is effected. Finally, the economic aspect of the problem must also be considered. In point of fact, the metal contained in the cup at the time of the stopping of the pouring generally represents a relatively large proportion of the metal of the part. After removal from the mold, this column of metal must be detached. It can be recovered and recycled but as the cost of remelting is proportional to the weight of the material to be recycled, a decrease in this quantity as a result of an accurate adjustment of the control for the stopping of the pouring represents a substantial decrease in the cost of manufacture of the parts.
Customarily, the stopping of the pouring when the mold is full is a manual operation. The founder visually notes at what moment the mold is full by observing the reactions of the surface of the metal in the cup as a function of the rate of flow of the stream falling from the casting ladle into the cup. In view of the time of human response, the metal actually ceases to flow into the mold only a certain time after complete filling has been detected, so that the manual control of the righting of the ladle, or of the closing of the ladle stopper, or of the closing of the discharge in the case of pressure ladles always leads to a certain loss of metal upon each pouring operation.
It has already been attempted to provide devices which detect the end of the filling and automatically stop the pouring. However, up to now these devices have always formed part of dosaging techniques and required a special shape of the mold which harmonizes poorly with the other requirements of the technique of the foundry. Thus, it has already been contemplated to provide vents at places judiciously located in the mold and observe the appearance of the metal in these orifices, which signals the filling of the mold. However, it is frequently difficult to produce vents which can be used for this purpose. The vents are an additional cause of comsumption of metal and, because of fluid dynamics may have undesirable consequences on the quality of the parts, or even prevent parts from being produced without major difficulties.
It has also been contemplated to provide, at the top of the sprue cup, a sort of overflow area which is filled with metal when the level in the sprue cup exceeds a maximum value. However, with this known solution for the problem of automatically interrupting the pouring, it is not possible to detect situations where the overflow area becomes filled before the mold as a result of splattering of metal or as a result of an irregularity in the flow from the sprue cup towards the cavity of the mold.
Accordingly, an object of the present invention is to create a device for stopping the pouring operation which monitors and analyzes the dynamic parameters of the system formed of the metal stream flowing from the ladle and the content of the sprue cup so as to detect the moment at which the behavior of this system corresponds to the conditions of total filling of the mold and bring about the cessation of metal pouring, i.e., righting of the tilting casting ladle, the closing of the stopper of a bottom pour ladle, or the closing of the discharge valve of a pressure ladle so as to terminate the flow of the metal at the proper time.
For this purpose, the invention entails a process for automatically stopping the pouring of the molten metal from a movable lip-type ladle or a bottom-pour or pressure-type ladle into a foundry mold provided with a sprue cup, characterized by the fact that it comprises at least a remote measurement of the free surface of the metal in the sprue cup and the rate of flow of the pouring stream; the production of a filling signal by derivation and summation from these measurements, the filling signal manifesting a sharp fluctuation when the free surface of the metal rises in the cup as a result of the complete filling of the mold; the comparison of the filling signal with a pre-established instruction value; and, the emission of a flow cut-off signal when the filling signal reaches the instruction value.
Furthermore, the apparatus constructed in accordance with the invention comprises a detection system; an emitter of a fixed or variable reference signal; and, an electronic circuit. The detection system is adapted to supply continuously or at a sufficiently rapid rate to the electronic circuit input signals at least one of which is a level signal corresponding to the level of the metal in the sprue cup and at least one second flow signal corresponding to the rate of flow of metal falling into the sprue cup. The electronic circuit is adapted to produce a filling signal from the input signals, to compare the filling signal with the reference signal, and to emit a flow cut-off signal which acts directly or indirectly on the ladle control motor when the filling signal exceeds a given instruction value of the reference signal, the instruction value being either automatically produced or not by the system itself.